A typical surgical tourniquet system of the prior art includes an inflatable tourniquet cuff for encircling a patient's limb at a desired location and a tourniquet instrument for supplying the tourniquet cuff with gas at a pressure sufficient to stop the flow of arterial blood past the cuff and into the limb. The tourniquet cuff typically includes an inflatable portion communicating pneumatically through a cuff port with a cuff connector that is releasably attachable to the tourniquet instrument through an instrument connector and flexible instrument tubing. This releasable connection establishes a pneumatic passageway for pressurized gas to pass between the tourniquet instrument and the inflatable portion of the cuff.
Many types of surgical tourniquet systems, including tourniquet cuffs and tourniquet instruments, have been described in the prior art, such as those described by McEwen in U.S. Pat. No. 4,469,099, U.S. Pat. No. 4,479,494, U.S. Pat. No. 5,439,477 and by McEwen and Jameson in U.S. Pat. No. 5,556,415 and U.S. Pat. No. 5,855,589. Many prior-art tourniquet instruments include a pressure regulator to increase and decrease the pressure of gas in the pneumatic passageway at the instrument end of the passageway to maintain the pressure in the inflatable portion of the cuff near a reference pressure that is above a minimum pressure required to stop arterial blood flow past the cuff during a time period suitably long for the performance of a surgical procedure. Some tourniquet instruments of the prior art, as described for example by McEwen in U.S. Pat. No. 4,469,099, include audio-visual alarms to promptly alert users to any significant over-pressurization or under-pressurization of a connected tourniquet cuff away from a selected tourniquet reference pressure, and include audio-visual alarms to alert users to any excessive periods of pressurization of a connected cuff, because the surgical literature clearly shows that such conditions are hazardous and are associated with increased probabilities of tourniquet-related injuries to patients. A few tourniquet systems of the prior art, such as those described by McEwen in U.S. Pat. No. 4,479,494 and U.S. Pat. No. 5,439,477, include physiologic transducers to help automatically determine the minimum and safest tourniquet reference pressure required to stop arterial blood flow in the limbs of individual patients undergoing specific surgical procedures.
In many tourniquet systems of the prior art, a pressure transducer located within tourniquet instrument is employed to sense the pressure of gas at the instrument end of the pneumatic passageway between the instrument and the tourniquet cuff, and that pressure is displayed for surgical staff as an estimate of the actual tourniquet cuff pressure and is employed by the pressure regulator of the tourniquet instrument. In such systems, the pressure transducer senses cuff pressure indirectly and remotely from the tourniquet cuff through long and flexible instrument tubing and an instrument connector. Accordingly, the accuracy of the estimated cuff pressure may be affected by partial or complete obstructions of the pneumatic passageway within the tourniquet instrument, instrument tubing, instrument connector and within the tourniquet cuff.
In prior-art tourniquet systems where cuff pressure is estimated remotely by a pressure transducer located within the tourniquet instrument, a variety of hazards may arise. For example, a complete obstruction may allow the actual pressure in the inflatable portion of the cuff to decrease substantially below the desired tourniquet pressure to a level where the cuff may be completely depressurized, or to increase substantially above the desired tourniquet pressure, without any indication to the surgical staff. In effect, the monitoring and regulation of cuff pressure may stop at the location of the obstruction. Also, any complete obstruction may render ineffective any audio-visual safety alarms of a connected prior-art tourniquet instrument intended to warn of hazardous over-pressurization or under-pressurization of the cuff, such as the safety alarms described by McEwen in U.S. Pat. No. 4,469,099. As another example, a partial obstruction may increase the pneumatic flow resistance at the location of the partial obstruction, and thus may reduce the ability of a connected tourniquet instrument to accurately and rapidly indicate changes in the actual cuff pressure and to rapidly and accurately regulate cuff pressure. Also, prior-art tourniquet systems in which cuff pressure is estimated remotely by a pressure transducer located within the tourniquet instrument may not be capable of detecting and responding rapidly, safely and appropriately to interruptions and large leaks caused by unanticipated malfunctions or failures of any of the pneumatic components forming the pneumatic passageway.
To improve safety and performance, some tourniquet systems of the prior art, often called dual-port tourniquet systems, establish two separate pneumatic passageways between the tourniquet instrument and the inflatable portion of the cuff. In one dual-port tourniquet system of the prior art, described in U.S. Pat. No. 4,469,099, the pneumatic pressure regulation elements within the tourniquet instrument communicate with the inflatable portion of the tourniquet cuff through one pneumatic passageway, and a pressure transducer within the tourniquet instrument communicates pneumatically with the inflatable portion of the cuff through a separate pneumatic passageway. Under normal operating conditions, this provides surgical staff with a more accurate indication of cuff pressure and enables the tourniquet instrument to increase the accuracy and speed of cuff pressure regulation. However, such dual-port tourniquet systems still sense cuff pressure by means of a pressure transducer located within the tourniquet instrument and thus their accuracy, performance and safety may be affected by flow resistances, partial obstructions, complete obstructions, interruptions and large leaks within their dual pneumatic passageways.
Tourniquet cuffs of the prior art can be grouped into three broad categories by their intended usage: (1) reusable tourniquet cuffs manufactured for usage outside the sterile surgical field in multiple surgical procedures, and for cleaning by users between successive procedures; (2) reusable tourniquet cuffs manufactured for usage within the sterile surgical field in multiple surgical procedures, and for cleaning and sterilization by specified sterilization processes between successive procedures; and (3) disposable tourniquet cuffs manufactured as sterile products suitable for usage within the sterile surgical field in one surgical procedure, and for disposal after the procedure.
Tourniquet cuffs of the prior art manufactured for use as sterile products within the sterile surgical field typically have long ports between the cuff connectors and the inflatable portions of such cuffs, allowing such cuffs to be applied and used within the sterile surgical field and to be connected to non-sterile tourniquet instrument connectors and non-sterile instrument tubing outside the sterile field. However, such long ports may interfere with the application of the cuff to the limb or may inadvertently make contact outside of the sterile field during cuff application and may thus contaminate the sterile cuff or surgical personnel. For certain surgical procedures, the desired sterile field may be very large and even very long ports of arbitrary lengths determined by the manufacturer may not be sufficiently long to extend beyond the desired sterile field. Also, including long ports in prior-art cuffs intended for use in a sterile surgical field adds to their cost of manufacture, an important consideration if the cuff is intended for disposal after a single surgical procedure. Also, increasing the lengths of the ports of sterile cuffs and sterilizable cuffs of the prior art to allow their connection to non-sterile instrument connectors and instrument tubing may increase pneumatic flow resistance, may affect the accuracy of cuff pressure indication and regulation, and may increase the likelihood of partial or complete occlusions of the pneumatic passageway, as described above.
In U.S. patent application Ser. No. 11/153,667 McEwen et al. describe a tourniquet cuff that has minimal flow restrictions within the pneumatic passageway of the cuff under normal operating conditions, that has a substantially reduced likelihood of partial or complete obstructions or interruptions of the pneumatic passageway within the cuff under foreseeable operating conditions, that can indicate exposure of the cuff to one or more external agents that are capable of affecting the integrity of the pneumatic passageway of the cuff before use, and that can be manufactured economically. However, McEwen et al. Ser. No. 11/153,667 does not address hazards that may arise due to flow restrictions and partial or complete obstructions of the portion of the pneumatic passageway external to the tourniquet cuff that are within the tourniquet instrument, the instrument tubing and the instrument connector.
In U.S. Pat. No. 6,682,547 McEwen et al. describe a tourniquet cuff having identification means indicative of a physical characteristic of the cuff and detectable by a connected tourniquet instrument. In U.S. Pat. App. Pub. US 20030167070 A1, McEwen et al. describe an adaptive tourniquet cuff system in which a tourniquet cuff carries identification means indicative of a physical characteristic of the cuff and in which a connected tourniquet instrument may automatically detect the physical characteristic of the cuff and adapt its operation in response to the detected physical characteristic. McEwen US 20030167070 A1 also describes the identification by a tourniquet instrument of prior exposure of a connected cuff to a potentially hazardous re-sterilization process. In U.S. patent application Ser. No. 11/153,667 McEwen et al. describe a disposable tourniquet cuff having means visually detectable by a user and automatically detectable by a connected tourniquet instrument to indicate exposure of the cuff to re-sterilization processes, indicating re-sterilization and possible reuse of a cuff originally manufactured and supplied as a sterile, single-use product. However, McEwen et al. '547, McEwen et al. US 20030167070 A1 and McEwen et al. Ser. No. 11/153,667 do not describe means for limiting the usage of a specific tourniquet cuff so that its usage does not exceed a safe usage limit for that cuff, to improve safety.
In the U.S. patent application Ser. No. 11/198,565, (hereafter the “Parent Application”) of which the present application is a continuation-in-part, McEwen et al. describe apparatus for appropriately limiting the usage of a specific tourniquet cuff so that its usage does not exceed a safe usage limit for that cuff, to improve safety. For example, the apparatus of the Parent Application can limit the number of usages of a specific non-sterile, reusable tourniquet cuff so that usage of the cuff does not exceed a safe maximum number. Also, the apparatus of the Parent Application can limit the usage of reusable tourniquet cuffs manufactured as re-sterilizable to usage and re-sterilization within safe limits, including for example limiting the cumulative inflation time, the maximum inflation pressure, the number of cycles of usage and re-sterilization, or the overall duration of usage from time of manufacture due to ageing of cuff materials. Further, the Parent Application also describes apparatus that can limit the usage of a single-use tourniquet cuff to usage within safe usage limits, and to usage in only one surgical procedure, without relying on the detection of re-sterilization to indicate possible reuse, because some users may attempt to reuse single-use cuffs as non-sterile cuffs, without exposing them to re-sterilizing agents and re-sterilization processes between successive usages. The apparatus of the Parent Application also describes a tourniquet instrument connector containing a cuff usage register interface that is located within a predetermined distance from the tourniquet cuff containing a cuff usage register so that cuff usage records can be read from, and written into, the register.